"It changed course after Kota Bharu and took a lower altitude. It made it into the Malacca Strait," the military official, who has been briefed on investigations, told Reuters.

While there is still no confirmation that the Boeing 777-200 crashed, aviation experts have put forward possible causes of its disappearance including a terrorist attack, extreme turbulence, human error or even suicide.

The Malaysian authorities initially said flight MH370 disappeared about an hour after it took off from Kuala Lumpur International Airport (KLIA), as it flew over the South China Sea, south of Vietnam's Ca Mau peninsula.

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Malaysia Airlines Flight Disaster In Pictures

Malaysia Airlines Flight Disaster In Pictures

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Grieving relatives (C) of passengers on Malaysia Airlines flight MH370 hold placards as they march towards the Malaysian embassy in Beijing on March 25, 2014. Scores of angry relatives of the Chinese passengers aboard Flight MH370 set out on a protest march to the Malaysian embassy in Beijing on March 25 to demand more answers about the crashed plane's fate. AFP PHOTO/ GOH CHAI HIN (Photo credit should read GOH CHAI HIN/AFP/Getty Images)